1. Field of the Invention
The present invention relates to a power integrated circuit device, and more particularly, to a power integrated circuit device having an embedded high side-power switch.
2. Description of the Related Art
Integrated circuit devices can be classified into integrated circuit devices operating at a low voltage (e.g., 30V or less) and power integrated circuit devices operating at a high voltage (e.g., 100V or more). Although high voltages are applied to the power integrated circuit devices, the power integrated circuit devices must normally operate without failure. Thus, the power integrated circuit devices have different structures from the integrated circuit devices operating at low voltages. Furthermore, is difficult to incorporate or embed semiconductor devices operating at a very high voltage (e.g., 600V) in integrated circuit devices. Thus, the very high voltage semiconductor devices are separate from integrated circuit devices and must be externally connected thereto. These problems with previous designs are explained in more detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic diagram illustrating a power integrated circuit device 111 to which high-side and low-side power switches 121 and 125 are connected externally. Referring to FIG. 1, the high-side and low-side power switches 121 and 125 are N-channel metal-oxide semiconductor field-effect transistors (MOSFETs)
In a typical implementation for the high-side power switch 121 performing a switching operation, a very high voltage HVDD, for example, of 600V, is connected to a drain of the high-side power switch 121, and substrate voltage Vs (or a ground voltage GND) of a high voltage region is connected to a source of the high-side power switch 121. Since a very high voltage is connected to the high-side power switch 121, the high-side power switch 121 must be capable of enduring the very high voltage. Thus, it is difficult to embed the high-side power switch 121 in the power integrated circuit device 111. As such, the high-side power switch 121 is implemented separately from the power integrated circuit device 111.
FIG. 2 is a cross-sectional view of a conventional power integrated circuit device 201 in which the high-side power switch 121 shown in FIG. 1 can be embedded. Such a power integrated circuit device 201 shown in FIG. 2 is disclosed in U.S. Pat. No. 4,866,495.
Referring FIG. 2, the power integrated circuit device 201 includes a semiconductor substrate 211, an epitaxial layer 221, a body area 231, a source area 235, a top area 241, a drain area 251, a source electrode 271, a gate electrode 273, and a drain electrode 275.
Here, the source area 235, the gate electrode 273, and the drain area 251 constitute the high-side power switch 121.
When a predetermined voltage is applied to the drain electrode 275 and a voltage applied to the gate electrode 273 is equal to or exceeds a threshold voltage of an N-channel MOSFET compared to a voltage applied to the source electrode 271, the high-side power switch 121 is turned on. When the high-side power switch 121 is turned on, a current flows from the drain electrode 275 to the source electrode 271. Here, if the body area 231 is deeply formed into the epitaxial layer 221, a current path readily forms between the body area 231 and the semiconductor substrate 211. Thus, a substantial current may flow from the body area 231 to the semiconductor substrate 211. This phenomenon is known as “punch-through.” When punch-through occurs, the high-side power switch 121 fails to perform the switching operation normally. Therefore, in order to avoid or prevent punch through from occurring, the body area 231 of the high-side power switch 121 can be thinly formed into the epitaxial layer 221.
However, if the body area 231 is thin, a pinch resistance of the source area 235 is reduced. As a result, a displacement voltage dV/dt deteriorates. More specifically, a current characteristic of the high-side power switch 121 can be expressed by Equation 1 as follows:
                    I        =                  C          ×                                    ⅆ              V                                      ⅆ              t                                                          (        1        )            where I denotes a displacement current, C denotes a capacitance, and dV/dt denotes a displacement voltage.
As shown in Equation 1, the displacement current I is formed by the displacement voltage dV/dt and flows through the body area 231 to the source electrode 271. A parasitic transistor among the source area 235, the body area 231, and the epitaxial area 221 may conduct. Thus, the high-side power switch 121 does not operate normally as a power switch. In other words, the displacement voltage dV/dt deteriorates.